Hi, This series is based on [0]. This patchset adds support for case-insesitive file names lookups in tmpfs. The main difference from other casefold filesystems is that tmpfs has no information on disk, just on RAM, so we can't use mkfs to create a case-insensitive tmpfs. For this implementation, I opted to have a mount option for casefolding. The rest of the patchset follows a similar approach as ext4 and f2fs. * Use case (from the original cover letter) The use case for this feature is similar to the use case for ext4, to better support compatibility layers (like Wine), particularly in combination with sandboxing/container tools (like Flatpak). Those containerization tools can share a subset of the host filesystem with an application. In the container, the root directory and any parent directories required for a shared directory are on tmpfs, with the shared directories bind-mounted into the container's view of the filesystem. If the host filesystem is using case-insensitive directories, then the application can do lookups inside those directories in a case-insensitive way, without this needing to be implemented in user-space. However, if the host is only sharing a subset of a case-insensitive directory with the application, then the parent directories of the mount point will be part of the container's root tmpfs. When the application tries to do case-insensitive lookups of those parent directories on a case-sensitive tmpfs, the lookup will fail. For example, if /srv/games is a case-insensitive directory on the host, then applications will expect /srv/games/Steam/Half-Life and /srv/games/steam/half-life to be interchangeable; but if the container framework is only sharing /srv/games/Steam/Half-Life and /srv/games/Steam/Portal (and not the rest of /srv/games) with the container, with /srv, /srv/games and /srv/games/Steam as part of the container's tmpfs root, then making /srv/games a case-insensitive directory inside the container would be necessary to meet that expectation. * Testing I send a patch for xfstests to enable the casefold test (generic/556) for tmpfs.[1] The test succeed. You can test this patchset using: sudo mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt/ And making a dir case-insesitive: mkdir mnt/dir chattr +F mnt/dir [0] https://lore.kernel.org/linux-fsdevel/20210323195941.69720-1-andrealmeid@xxxxxxxxxxxxx/ [1] https://lore.kernel.org/fstests/20240823173008.280917-1-andrealmeid@xxxxxxxxxx/ André Almeida (5): tmpfs: Add casefold lookup support tmpfs: Add flag FS_CASEFOLD_FL support for tmpfs dirs tmpfs: Create casefold mount options tmpfs: Expose filesystem features via sysfs docs: tmpfs: Add casefold options Documentation/filesystems/tmpfs.rst | 37 +++++ include/linux/shmem_fs.h | 7 +- mm/shmem.c | 205 ++++++++++++++++++++++++++-- 3 files changed, 238 insertions(+), 11 deletions(-) -- 2.46.0
